In order to find a hypothetical enzyme (cytochrome c synthetase) which would catalyze the covalent bonding of heme to apocytochrome c, Rhodospirillum rubrum is chosen as the enzyme source and the source of the apo-protein. Preliminary experiments have been carried out, including isolation of cytochrome c2 from the organisms, test of stability of apo cytochrome c (horse heart) and C-monocarbamoylation of yeast cytochrome c, presumably at the alpha-amino group.